The present invention relates to a process for producing a crosslink-cyclized cyclopentadiene, a crosslink-cyclized cyclopentadiene, a dihalobis(xcex7-crosslink-cyclized cyclopentadienyl)metal compound containing the crosslink-cyclized cyclopentadiene, and a process for producing the same.
Cyclopentadienes are widely used not only as monomers for producing various polymers but also in the production of metallocene compounds of transition metals such as titanium, zirconium and hafnium. The metallocene compounds are widely utilized as effective ligand components of olefin polymerization catalysts.
Regarding the conventional production of a crosslink-cyclized cyclopentadiene, for example, with respect to the process for producing 1,3-dimethylcyclopentadiene, Japanese Patent Laid-open Publication No. 62(1987)-72630 describes a process comprising reacting dicyclopentadiene with methanol in the presence of an alkali metal oxide. However, this process has a drawback in that the desired product cannot be efficiently obtained due to, for example, by-products of position isomers.
Further, Japanese Patent Laid-open Publication No. 3(1991)-215437 describes a process comprising performing a vapor-phase cyclization dehydration of 5-methyl-5-hexen-2-one in the presence of a catalyst such as alumina. However, this process has drawbacks in that the raw materials are expensive and that the reaction must be performed in a vapor phase at such high temperatures as over 200xc2x0 C. to thereby necessitate special apparatus.
Still further, Japanese Patent Laid-open Publication No. 8(1996)-208533 describes a process for producing a cyclopentadiene, comprising performing a cyclization dehydration of an unsaturated carbonyl compound in the presence of a solid acid catalyst in a vapor phase. However, this process also has a drawback in that the reaction comprises a cyclization dehydration in a vapor phase and the reaction temperature is as high as 330 to 430xc2x0 C. (as indicated in working example portions) to thereby necessitate special apparatus.
With respect to a crosslink-cyclized cyclopentadiene of the general formula: 
the formula has been shown in, for example, Japanese Patent Laid-open Publication No. 9(1997)-132537 in connection with the use as ligands of metallocene catalysts for olefin polymerization. However, there is no particular teaching having been published as to a crosslink-cyclized cyclopentadiene wherein both R1 and R2 are alkyl groups and as to the process for producing the same. Further, there is no particular synthetic example published for such a compound as far as the inventors"" investigations have been made.
The present invention has been made with a view toward solving the above problems of the prior art. It is an object of the present invention to provide a process for producing a crosslink-cyclized cyclopentadiene with high yield under mild conditions without the need to install special apparatus. It is another object of the present invention to provide a crosslink-cyclized cyclopentadiene comprising a cyclopentadiene substituted with two alkyl groups.
It is further objects of the present invention to provide a dihalobis(xcex7-crosslink-cyclized alkyl-substituted cyclopentadienyl)metal compound wherein the above crosslink-cyclized cyclopentadiene is incorporated and to provide a process for producing the same.
The inventors have made extensive and intensive studies with a view toward solving the above problems. As a result, they have found a novel process for producing a crosslink-cyclized cyclopentadiene with high yield under mild conditions without the need to install special apparatus, wherein a crosslink-cyclized cyclopentenone is reacted with an alkali metal hydride to thereby reduce the same and wherein the thus obtained crosslink-cyclized cyclopentenol is reacted with a dehydrating agent to thereby reduce the same.
In addition, the inventors have specifically found a novel crosslink-cyclized cyclopentadiene comprising a cyclopentadienyl substituted with two alkyl groups.
Moreover, the inventors have found a novel dihalobis(xcex7-crosslink-cyclized alkyl-substituted cyclopentadienyl)metal compound wherein the above crosslink-cyclized cyclopentadiene is incorporated and a process for producing the same. The present invention has been completed on the basis of these findings.
According to the first invention, there is provided a process for producing a crosslink-cyclized cyclopentadiene, comprising the steps of;
reacting a cyclopentenone of the general formula (I) with an alkali metal hydride; 
wherein each of R1 and R2 independently represents a hydrogen atom or a linear or branched saturated alkyl group having 1 to 6 carbon atoms, and n is an integer of 3 to 10,
to thereby reduce the cyclopentenone (reduction step A) into a cyclopentenol of the general formula (II): 
wherein R1, R2 and n are as defined above with respect to the general formula (I); and
reacting the cyclopentenol with a dehydrating agent to thereby dehydrate the cyclopentenol (dehydration step B) into a crosslink-cyclized cyclopentadiene of the general formula (III): 
wherein R1, R2 and n are as defined above with respect to the general formula (I), and the broken line in the 5-membered ring denotes that the 5-membered ring has two double bonds.
The alkali metal hydride is preferably an alkali metal borohydride compound, still preferably sodium borohydride or potassium borohydride. The reduction step A is preferably performed at xe2x88x9210 to 100xc2x0 C. The dehydrating agent is preferably a strong acid. The dehydration step B is preferably performed at xe2x88x9210 to 100xc2x0 C.
According to the second invention, there is provided a crosslink-cyclized cyclopentadiene of the general formula (IV): 
wherein each of R1 and R2 independently represents a linear or branched saturated alkyl group having 1 to 6 carbon atoms, n is an integer of 3 to 10, and the broken line in the 5-membered ring denotes that the 5-membered ring has two double bonds.
According to the third aspect of the present invention, there is provided a dihalobis(xcex7-crosslink-cyclized cyclopentadienyl)metal compound of the general formula (V): 
wherein each of R1 and R2 independently represents a linear or branched saturated alkyl group having 1 to 6 carbon atoms; n is an integer of 3 to 10; M represents Ti, Zr or Hf; and X represents a halogen atom selected from among a chlorine atom, a bromine atom, an iodine atom and a fluorine atom.
The dihalobis(xcex7-crosslink-cyclized cyclopentadienyl)metal compound of the general formula (V) according to the present invention is obtained by reacting a cyclopentadiene of the general formula (IV) with a metal halide; 
wherein R1, R2 and n are as defined above with respect to the general formula (V), and the broken line in the 5-membered ring denotes that the 5-membered ring has two double bonds,
this reaction being performed in the presence of a base.